Quantum-fluctuation-driven crossover from a dilute Bose-Einstein condensate to a macro-droplet in a dipolar quantum fluid

In a joint experimental and theoretical effort, we report on the formation of a macro-droplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions. By precise tuning of the s-wave scattering length below the so-called dipolar length, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of more than 10^4 atoms. Based on the study of collective excitations and loss features, we quantitative prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions. Finally, we perform expansion measurements, showing the evolution of the normal BEC towards a three-dimensional self-bound state and show that the interplay between quantum stabilization and three-body losses gives rise to a minimal expansion velocity at a finite scattering length.

@article{Chomaz2016,
title = {{Q}uantum-fluctuation-driven crossover from a dilute {B}ose-{E}instein condensate to a macro-droplet in a dipolar quantum fluid},
author = {L.~Chomaz and S.~Baier and D.~Petter and M.~J.~Mark and F.~Wächtler and L.~Santos and F.~Ferlaino},
journal = {Phys. Rev. X},
volume = {6},
issue = {4},
pages = {041039},
numpages = {10},
year = {2016},
month = {Nov},
abstract = {In a joint experimental and theoretical effort, we report on the formation of a macro-droplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions. By precise tuning of the s-wave scattering length below the so-called dipolar length, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of more than 10^4 atoms. Based on the study of collective excitations and loss features, we quantitative prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions. Finally, we perform expansion measurements, showing the evolution of the normal BEC towards a three-dimensional self-bound state and show that the interplay between quantum stabilization and three-body losses gives rise to a minimal expansion velocity at a finite scattering length.},
publisher = {American Physical Society},
doi = {10.1103/PhysRevX.6.041039},
url = {http://link.aps.org/doi/10.1103/PhysRevX.6.041039},
arXiv = {http://arxiv.org/abs/1607.06613}
}